PreambleIf
you are one of those audiophiles who doesn't take single-ended
triode amplifiers seriously, get ready for a paradigm shift. I
guess if you need one of those mega-power solid-state
monoliths to boost your ego and impress your audio buddies,
then a 3.5 Watt amp with a pair of 2A3 direct-heated triodes
just won't set your heart aflutter. I can understand that.
This is why I want to tell you about the Bel Canto SETi40
integrated amplifier.

The SETi40 has
all the credentials that the triode-maniac insists upon: pure
class A operation, zero negative feedback, and one
direct-heated power triode per channel, run hot and hard. But
in this case, the tube that Bel Canto's John Stronczer has
chosen to design with for the last fifteen years, is a radio
transmitting triode: the redoubtable 845. These tubes are
plentiful and cheap. A complete re-tube will cost about $200
after 8000 hours, or so.

The 845 is
from the same family of tubes, and is the same size, as the
211 triodes used in the Audio Note Ongaku. This is a big tube
and it is a good one. Pick it up. Handle it. An EL-34 pentode
is like a peashooter in comparison to this magnificent piece
of glass. Pause for a moment while holding the 845 in your
hand. It will make you feel like Ming the Merciless.

When the
SETi40 is switched on, you will be startled to see that the
tube heaters glow bright yellow-white like an incandescent
lamp. I think the U.S. Navy used the 845 in the transmitters
on PBY Catalina flying boats. If they didn't, they should
have. The fiercely glowing filaments would have kept the
radiomen warm on those long patrols over the Pacific.

DesignThe
Bel Canto SETi40 integrated amplifier is a highly refined
piece of technology that deserves our admiration for its level
of sophistication and ease of use. This isn't a home-brew
spam-can with a few holes punched in it for some oddball
triodes and junk-store transformers. Of course, you're going
to pay for this level of engineering, but you get a lot for
your money.

The unit
weighs about 30 kilos (65 lbs.) and most of that is devoted to
the amplifier's massive transformers. The case is heavy gauge
steel finished in black crinkle enamel. The effect is serious
and businesslike and more than a bit retro-cool. It reminds me
of the finish on those Bell & Howell slide projectors they
sold when Kodachrome was introduced in the early 1930s; or the
camshaft covers of a Ferrari GTO - take your pick. The message
is received loud and clear: we're here to stay. My favourite
styling cues, though, are the retro-tech rings-of-gold
encircling the massive 845 power triodes like something out of
an H. G. Wells novel. They are functional, too, protecting one
from the furious heat dissipated by the tubes' filaments,
while, at the same time, acting as heat sinks. They also
diffuse the glowing illumination of the power tubes in an
attractive and chic deco style. Finally, I must mention the
way in which the unit's transformers have been molded into
part of an organic whole. The transformer cover, with its
stolid left and right bastions conjoined by an artfully curved
façade, reminds me constantly and consistently of Frank
Lloyd Wright's design for Unity Temple in Oak Park, Illinois.
Why this should be, I cannot say precisely except that there
is something monumental about the design of the whole Bel
Canto SET line that touches my collective unconscious. Dare I
suggest that there is something here that reminds me of an
altar with candles glowing in the darkness?

If the owner
cares to look inside, he will find high quality components
well spread out on a 1/8th inch-thick fiberglass
printed circuit board. No hard-wiring for Bel Canto, contrary
to current fashion among other single-ended amplifier
manufacturers. "Why", I asked Bel Canto? "Better
sound", they claim. Using circuit boards, there are fewer
manufacturing inconsistencies - makes sense to me. I was
surprised, however, to see a bank of high-speed solid-state
rectifiers inside the SETi40. Some single-ended purists claim
that tube rectifiers are the only acceptable way to build a
power supply. This may be true when you are running 300Bs at
350 VDC, but when you are dealing with 1200 VDC and selling to
the public don't mess with Mother Nature.

FeaturesThe
SETi40 was designed as a remote-controlled integrated version
of the Bel Canto SET 40. It produces 40 Watts per channel over
a bandwidth of 5Hz to 35kHz, and is said to have exceptionally
low distortion, primarily second order harmonic. There are
three gold-plated RCA input jacks on the rear panel as well as
a robust switch for selecting 4 or 8 Ohm output impedance. The
five-way binding posts are excellent quality. The on/off
switch on the rear panel sets the amplifier to standby mode.
After a very brief wait in standby, the amp can be fully
powered up.

The
remote-control functions are comprehensive: volume, balance,
mute, input selection and standby/on/off. Volume control is
accomplished with a very advanced analog Crystal 3310 chip
stepped attenuator. Changes in volume settings are displayed
via a red LED readout, large enough to be easily seen from the
listening position. Relays, closely located to the volume
chip, are used for input switching. All controls worked
silently, without clicks, pops, or thumps. I found the remote
control to be a worthwhile addition to the design and hope
that more manufacturers will incorporate one into their future
offerings.

The input
circuit uses pairs of 12AX7 tubes for each channel in a
modified series-regulated push-pull (SRPP) configuration. Some
single-ended gurus consider this arrangement to be less than
optimal. I won't attempt to argue the point here. Bel Canto
has some good reasons for going this route, as outlined in a
white paper on the company's web site. The SETi40's output
power tubes are self-biasing and, therefore, never need to be
adjusted, even after replacement.

Nuts and BoltsFor
many reasons, the Bel Canto SETi40 is a very impressive
amplifier. I have already outlined the technical
sophistication and the aesthetic appeal of the design. What
impresses me most about the product, however, is simply this:
it is single-ended and it will drive my Quad ESL-63s
with ease. Finally, we have an SE amp that will drive most
real-world audiophile speakers - the speakers that music
lovers actually own and enjoy - with credible volume and
dynamics.

Now, I present
the case for single-ended amplification.

Do you
remember Andy Granatelli's STP turbine cars that raced at
Indianapolis in the late 1960s? A turbine engine is a
cigar-shaped tube with a longitudinal shaft to which a spiral
of many small perpendicular fan blades is attached. The blades
at the front of the engine draw in air. Fuel is injected
directly into the combustion chamber, where it is ignited, and
the heat from the inlet air and expanding exhaust gasses cause
the blades to spin at speeds over 50,000 R.P.M. At
Indianapolis, the turbine car was superior to the rest of the
field because the engine was smoother, more powerful, and
consistently at the peak of its power band. That's what a
class A, single-ended amplifier is like: a turbine at full
bore. The volume control on your pre-amp is your rev-limiter,
and the music signal your throttle and brakes.

Push-pull
designs are cheaper and easier to implement for a given power
output but they suffer from a number of lamentable
limitations, as did the front-engine Offenhauser engine cars
that thrilled the crowds at The Brickyard.

Some degree of
negative feedback is used in almost every push-pull amplifier
because it reduces measured distortion. It seems, however,
that negative feedback introduces some subtle, unmeasurable
distortions, which are manifest to the ear as poor timing,
dynamic compression, and alteration of instrumental timbres.
The harmonic distortions of the single-ended amplifier are
primarily second-order, a point on the harmonic spectrum that
the ear finds quite acceptable. This is why single-ended
amplifiers have no need for negative feedback. Continuing with
my automotive analogy, I like to imagine negative feedback as
steering that lags behind the driver's inputs so that he is
constantly over and under correcting in an attempt to maintain
a perfect line while traveling at speed. Perfectly direct
steering is the equivalent of zero negative feedback.

The last point
I want to make is that a push-pull amp must have a
phase-splitting front end. The input signal is divided into
positive and negative halves in order to drive the pairs of
output tubes that are chugging up and down like a pair of
pistons. The necessarily imperfect blending of the positive
and negative signal halves causes a blurring and veiling in
the output stage that reminds me of a carbureted piston engine
with a timing problem.

ListeningThe
Bel Canto SETi40 sounds so different from the other tube
amplifiers I have been listening to that I wasn't sure I could
muster the vocabulary to tell you about it. That's why I
developed the turbine analogy in the previous section, because
that was the overwhelming impression I had, and still have, of
this amplifier. The differences are subtle, certainly, but
undeniably real.

The grainless
purity of the SETi40's treble lets one forget the medium and
become absorbed in the music. Thanks to its lack of negative
feedback, the SETi40 allows one to listen to the music in a
new way. Rather than being a distant spectator, we find
ourselves participating in the musical event. The emotive
intention of the artist is clarified and illuminated by this
amplifier in a unique and extraordinary fashion. This struck
me once at a concert by flute virtuoso, Jean-Pierre Rampal. I
thought to myself, 'He is the music!'. And that's what
it's like listening to the Bel Canto. The most subtle artistic
nuances are so delicately rendered that one feels the very
presence of the musician. And that extends to the recording
environment as well.

Take, for
example, one of the finest Beethoven Fifth Symphonies ever
recorded, Erich Kleiber conducting the Concertgebouw Orchestra
(Decca LXT-2851). Even though this is a mono recording, the
sonic signature of the hall is easily discernible. And need I
say anything about dynamics, drive, and timing? No, this is
what we call musical artistry.

Another record
that revealed itself to be stunning was the Elgar Violin
Concerto with the RPO under Sir Charles Groves (EMI ASD
2883) featuring Hugh Bean on solo violin. This is, perhaps,
Bean's signature recording, and certainly one of the best ever
engraved on vinyl. The liquid purity of the sound of the
violin made me realize how choppy and mechanical push-pull
amplifiers sound. The difference is, as the French say, epouvantable.

This natural
smoothness can be ruthlessly revealing, though. Listening to
the Vaughan Williams, Academy of St. Martin in the
Fields/Marriner collection, Greensleeves (Super
Analogue KIJC-9109) gave me the uneasy feeling that some
equalization had been applied to the Japanese stamper.
Nevertheless, The Lark Ascending, featuring Iona Brown
on solo violin, sounded sublimely sensual. On one hand we have
the delicate, spiraling solo part, and on the other, the rich,
resonant cello and bass choirs showcased by the full-throated
lower reaches of the magnificent 845 triodes.

ConclusionIf
you want further examples of the musicality of the Bel Canto
SETi40, have a look at the first installment of my series on
the classic London Blueback LPs published recently in
Audiophilia. All of the listening for this article was done
with the benefit of the Bel Canto.

The SETi40 is
a great amplifier, especially if you are wed to a pair of Quad
ESL-63s and want single-ended sound. The 845 is a powerful,
masculine tube that is capable of driving the Quads (as well
as more conventional loudspeakers) to realistic levels without
stress. Needless to say, I recommend the Bel Canto SETi40
without reservation.